Spooled torsion spring for securing head strap in head-mounted display

An apparatus for adjusting a head strap in a head-mounted display (HMD) includes a rigid body, a flexible link, a spool, a torsion spring, a driving gear assembly a rigid shaft, a rod, and a holder. The driving gear assembly includes a first gear and a second gear. The torsion spring applies a biasing torque onto the driving gear assembly. Based on the biasing torque from the torsion spring, the driving gear assembly rotates. The spool rotates relative to the rigid body to wind the flexible link onto the spool. A biasing torque adjustment mechanism may be provided to adjust the biasing torque applied by the torsion spring.